Cerebrovascular accumulation of the amyloid b-protein (Ab), a condition known as cerebral amyloid angiopathy (CAA), is a common small vessel disease in the elderly, an important driver of vascular cognitive impairment and dementia (VCID) and a prominent comorbidity of patients with Alzheimer?s disease (AD). Despite the growing recognition of the contribution of CAA to VCID, early and accurate diagnosis of this condition has remained elusive and largely relies on neuroimaging modalities that are only effective in late stages of the disease. The current ?Boston MRI criteria? for CAA are based on the presence of multiple lobar microbleeds in the brain. However, the neuroimaging approaches are limited in that neuropathological findings demonstrate that abundant CAA is prevalent at early stages of disease without the presence of microbleeds, particularly in patients with AD. Thus, there is a need for biomarkers for early stages of disease prior to the presence of microbleeds detected by neuroimaging. The purpose of the is project is to fill in this void by developing and validating robust biological fluid markers for CAA. Recent work from our laboratories has identified novel candidate biomarkers that appear specific for CAA and mechanistically can be linked to the disease process and can be measured in biological fluids. These candidates were derived from a combination of biochemical and immunochemical approaches using potent and specific human cerebral vascular cell cultures and rodent models for CAA, and their presence has been confirmed in human CAA tissues. The overall hypothesis of this proposal is that these novel candidate biomarkers are unique and specific for CAA and will facilitate in an early and accurate diagnosis of CAA- related small vessel disease. There are two specific aims of this project. First, we will study the trajectory of CAA biomarkers in a transgenic rat model for CAA from the presymptomatic phase (prior to microbleeds) to the symptomatic phase (prominent microbleeds). This model provides the powerful and unique prospect to investigate the longitudinal expression of CSF and serum biomarkers in relation to the progression of disease severity, particularly in prodromal states, an opportunity that is not available in humans. Further, our CAA rat model will be used to identify additional candidate biomarkers using complementary proteomic approaches. Lastly, comparative studies will be performed using rat models of parenchymal plaque amyloid pathology or hypertension/stroke, another common cerebral small vessel disease, to further establish the specificity of CAA biomarkers. Second, we will further characterize, develop and validate assays for candidate protein biomarkers for the diagnosis of CAA including: intact and derivatives of Ab40 peptide, the chief component of cerebral vascular amyloid accumulation, heat shock protein B2 (HSPB2), and urokinase-type plasminogen activator (uPA). A priority of our plan is to share our data, provide developed assays, key reagents, patient samples and rat models to other groups and consortiums to advance small vessel disease biomarker development.